Records from French Guiana, Guyana, Suriname and Venezuela this species are probably P. orbignyi (Carvalho et al. 2003). Live and fixed specimens are easily mistaken with P. orbignyi, P. humerosa and juveniles of P. brachyura (Charvet-Almeida and Almeida pers. obs.). P. histrix is also often misidentified as Potamotrygon sp. or Potamotrygon cf. histrix ("arraia cururu" from the Negro River basin) (Araújo pers. com.).

The lectotype designated by Castex (1969) is not considered valid (Rosa 1985, Carvalho et al. 2003).

Justification:
The Porcupine River Stingray (Potamotrygon histrix) is a small, common but poorly known freshwater stingray from the Paraná and Paraguay River basins. Its conservation status is uncertain due to the sparse life history and population data available. It probably undertakes seasonal migrations and very few pregnant females have been observed so far. It is harpooned for food and is also captured for the ornamental fish trade, especially juveniles. Habitat degradation through various human activities is probably the main threat facing this species. Further studies and a re-assessment in the near future are highly recommended.

There is no life history or population data for this poorly known freshwater ray. The main area of occurrence for this species is apparently the Paraná-Paraguay River confluence, where it is considered relatively abundant (Soto pers. obs.).

Achenbach and Achenbach (1976) indicate that this species is more abundant in the Paraná and Colastiné Rivers and seems to prefer "open waters" (probably preferring to wider areas instead of small streams). Seasonal migrations (upstream of the Paraná River) have also been indicated (Achenbach and Achenbach 1976).

There is little information available on the life history of this species. Achenbach and Achenbach (1976) suggested that reproduction takes place in the upper portion of the Paraná River. Newborns have been observed in early summer and adults with of 30-40 cm disc width (DW) are common. The maximum weight observed is ~15 kg. Two females from the lower Paraná River (33 and 36 cm DW) contained nine and six embryos, respectively (Soto unpublished data).

Achenbach and Achenbach (1976), in general observations considering this and other species of potamotrygonids in the mid Paraná River system, indicated that neonates feed on plankton and then gradually change their diet to small molluscs, crustaceans (crabs), insect larvae, small fish and other food items.

This and other southern freshwater stingray species are taken as a food source and are considered to have delicious meat. They are harpooned by fishermen when sighted resting in shallow water.

There is a small amount of fishing for the more attractively patterned juveniles to supply the ornamental fish trade. This species is illegally exported from Brazil and no information is available regarding its captures for the international trade (Araújo et al. 2004).

The major threats are likely to be from habitat degradation caused by the damming of the Paraná River system for navigation and hydroelectric plants, and the construction of many ports along the river (infrastructure development). Agriculture, various kinds of water pollution, human disturbance and intrinsic factors also are considered threats for this species.

Policy-based and research actions are required to protect this species. Habitat maintenance and conservation actions are also needed, such as creation and maintenance of protected areas. The construction of hydroelectric plants in the Paraná-Paraguay River system should be controlled. Education and public awareness of potamotrygonids is essential due to the negative image of these species. Monitoring and regulation of harvest levels and trade for ornamental purposes is also needed.